Several members of the C-C branch of the chemokine family have been strongly implicated in the generation of tissue eosinophilia during allergic inflammation, due to their potent and selective chemoattractant activity on eosinophils. Since eosinophils are believed to be responsible for the tissue damage observed in allergic diseases, an improved understanding of the factors responsible for their recruitment in vivo is imperative. We have developed an in vivo chemokine challenge model with which we characterized the tissue response to RANTES in humans. We noted a profound delay in eosinophil recruitment in nonallergic subjects as compared to allergic subjects. Studies described in Aim 1 are designed to test whether the state of eosinophil priming or CCR3 expression or function explain this result. Studies in following Aims will follow up on our recent exciting discovery that epithelial (Aim 2) and endothelial (Aim 3) cells express a functional CCR3, which to date has only been described on leukocytes, mast cells and microglial cells. We will study the regulation of CCR3 expression focusing on cytokine families that are relevant for allergic diseases, namely Th1 and Th2 cytokines. Functional studies will focus on cell migration, induction of adhesion molecule expression, cytokine production and proliferation. To provide further insight into the biology of this receptor, we will determine whether epithelial or endothelial CCR3 expression varies depending on disease status (allergic vs nonallergic ) and whether allergen challenge modulates the baseline expression in allergic subjects. This grant proposal will test the overall hypothesis that chemokine responsiveness in vivo is dependent on several factors. including leukocyte priming and expression and function of relevant chemokine receptors on leukocytes and parenchymal cells (such as epithelial and endothelial cells). Results of these studies are likely to provide insights into the mechanisms by which chemokines induce cutaneous cell recruitment and will likely identify entirely new biological effects of C-C chemokines.